Wobble drive mechanisms for reciprocating the cutter bar of a mowing device are described in such U.S. Pat. Nos. as 3,397,584; 3,444,676 and 3,463,018. Also, the use of resilient spring devices for storing and releasing energy during reciprocation of a sickle bar are shown in such U.S. Pat. Nos. as 14,046; 280,901; 280,902 and 1,078,101.
The capacity of agricultural combines may be increased by operation at higher ground speed, which requires higher frequency of reciprocation of its sickle bar cutter. The inertia related forces in the cutter mechanism increase with the square of the frequency of reciprocation. U.S. Pat. Nos. 4,342,186 and 4,342,187 assigned to the same assignee as the present invention describe a torsion spring coupled, wobble drive cutting mechanism whose resonant frequency is within the reciprocating frequency range at which the sickle is normally operated for crop cutting, thereby resulting in greatly reduced input torque requirement and conserving power and energy. In one embodiment the torsion spring is in the form of an elongated torsion bar in alignment with the axis of oscillation of the sickle operating lever, and preferably the torsion bar has zero stored energy at the midpoint of reciprocation of the sickle bar and stores energy as the sickle bar moves in either direction from the midpoint to the end of its stroke so the torsion bar releases its energy to the sickle bar as the sickle bar moves from the end of its stroke to the midpoint of its stroke.
Such torsion spring coupled resonant sickle drive mechanisms create a hazard to the operator if energy is stored in the torsion spring during shutdown of the drive mechanism since fingers could possibly be cut off by unexpected sickle bar motion after the combine is shut off, or the operator possibly could be injured from unexpected motion of the wobble drive mechanism or the belt drive therefor. A rock caught between the sickle cutter bar and the guard might hold the sickle bar away from its midpoint position, thereby resulting in stored energy in the torsion bar which cannot be seen and constitutes a danger which is not obvious to the operator. Alternatively, the cutter mechanism inertia might cause the sickle bar to stop at one end of its stroke, thereby resulting in maximum energy stored in the torsion spring.